Someone I know almost didn't graduate this semester because his advisor gave him all of his easy classes in the fall semester and made him take 18 credits of hard engineering classes this spring. My advisor didn't allow me to request a time override despite them only having a conflict of one hour on one day. I need both of those classes to graduate and I couldn't take the other section because it was during the same time of my other major class. Luckily, it was a blessing in disguise and I was able to take that class this summer at a community college which was way easier than taking it at my home institution
That reminds me of another important tip. 12 credits isn't full time unless you want to take 5+ years. You need 15/16 credits per semester average to actually graduate in 4 years.